Sulphostin and analogues of sulphostin represented by the following general formula (1) (where n is an integer of 0 to 3) are new organic compounds having a dipeptidyl peptidase IV inhibitory action. In particular, a compound represented by the following general formula (2) having the structure in which, in the general formula (1), n is 2, the configuration at C* is S, the configuration at P* is R, is described as sulphostin in the following literature.

These compounds are expected to be applied to medicines, such as an immunomodulator, a hormone regulator, an anti-HIV drug, an antiallergic drug, an antiinflammatory drug and an antirheumatic drug (WO99/25719).
In addition, as for preparation of the above compound, because a fermentation method has low productivity and is not suitable for mass production for the present, a preparation method by synthesis is reported (JP-A-2000-327689). The preparation method employs a process of activating an amide with the use of a super strong base under ultra low temperature (−78°C.) conditions, and then reacting phosphonyl chloride and liquid ammonia under similar temperature conditions, in the step of preparing phosphoric acid amide. In the step of resolution, chromatography is used, so that the resolution is imperfect thus making it difficult to provide a product of high purity. Accordingly, the above preparation method cannot produce a large amount of the above compound in an industrial scale.